US3662372A - Monitoring system for door stations - Google Patents

Abstract

A monitoring system for a plurality of remote door stations to indicate the status of each door. Each door operates in conjunction with two switches, both of which remain closed when the door is closed (Condition I). Only the first switch is opened when the door is legally opened (Condition II) whereas both switches are opened when the door is violated (Condition III). A central console is provided including relay-operated light indicators which are individually wired to the first switches located at the several stations and a relay-operated alarm device which is wired to the second switches in a series circuit. Also provided is a flasher unit coupled to the light indicators. The arrangement is such that when Condition I exists at any one station, the corresponding light indicator on the console gives steady illumination; when Condition II exists, the light indicator is caused by the flasher unit to operate periodically; and when Condition III exists, the alarm device is actuated and the light indicator is caused to operate periodically to call attention to a violation.

Description

United States Patent Levy [ 51 May 9, 1972 [54] MONITORING SYSTEM FOR DOOR STATIONS [72] lnventor: Marvin J. Levy, 2133 Kenwood Place,

Bellmore, N.Y. 11710 [22] Filed: Apr. 23, 1969 [21] App1.No.: 818,677

[52] US. Cl ..340/274, 340/256, 340/282 [51] Int. Cl. ..G08b 13/08 [58] Field of Search... ..340/274, 227.1, 147 LP, 256

[56] References Cited UNITED STATES PATENTS 3,537,094 10/1970 Hawkins et a1. ..340/274 2,994,858 8/1961 Coffer ..340/227.1 3,513,466 5/1970 lsaacs ..340/274 Primary Examiner-John W. Caldwell Assistant Examiner-William M. Wannisky Attorney-Michael Ebert [5 7] ABSTRACT A monitoring system for a plurality of remote door stations to indicate the status of each door. Each door operates in conjunction with two switches, both of which remain closed when the door is closed (Condition 1). Only the first switch is opened when the door is legally opened (Condition 11) whereas both switches are opened when the door is violated (Condition 111). A central console is provided including relayoperated light indicators which are individually wired to the first switches located at the several stations and a relayoperated alarm device which is wired to the second switches in a series circuit. Also provided is a flasher unit coupled to the light indicators. The arrangement is such that whenCondition 1 exists at any one station, the corresponding light indicator on the console gives steady illumination; when Condition 11 exists, the light indicator is caused by the flasher unit to operate periodically; and when Condition lll exists, the alarm device is actuated and the light indicator is caused to operate periodically to call attention to a violation.

7 Claims, 2 Drawing Figures PATENTEDM 9 I972 SHLET 1BF 2 AWL W YUM Nam MONITORING SYSTEM FOR DOOR STATIONS BACKGROUND OF INVENTION This invention relates generally to monitoring systems for indicating at a central console the status of a plurality of remote stations, and more particularly to a system wherein each station is provided with door switches and the monitor console, which is coupled to the switches, indicates whether the door is closed or whether it has been legally opened or violated.

With the growing crime rate in the United States, an increasing need has arisen for protective alarm devices. Thus in factories, warehouses and in other establishments which are accessible through doors located at dispersed points in the structure, it is the practice to install at each station a protective unit which sets off an alarm when a door violation occurs. In one such device, a key-operated door lock is equipped with a switching circuit which, when the door is illegally opened, either from the inside or the outside, acts to set off an alarm.

Inasmuch as the door may be unattended, by the time security personnel locate and reach the violated door, the intruder may have escaped. It becomes desirable, therefore, to provide a central monitor wired to the various doors to indicate the existence of a violation, so that a guard may then be quickly dispatched to the proper station to intercept the intruder.

In a conventional monitoring system for this purpose, a bank of lights or other indicators on a monitor console is wired to door switches at the various stations, current to operate the indicators flowing through the station switches associated therewith. In some instances, the wires may be extended for hundreds of yards to points remote from the console, in which event the wires introduce substantial resistance in the indicator circuit. This resistance may give rise to an unreliable or defective operation, for the resultant voltage impressed across the relays operating the indicator may be well below the rated level and insufficient to actuate the relays.

BRIEF DESCRIPTION OF INVENTION In view of the foregoing, it is the main object of this invention to provide an improved monitoring system having a central console operating in conjunction with a plurality of remote door stations to indicate the status of each station.

MOre particularly, it is an object of the invention to provide a system of the above type in which the status of each station is indicated by means of individual light indicators and an alarm device common to all stations, whereby the fact that the door is closed at any station (Condition 1) is indicated by a steady light; the fact that the door has been legally opened (Condition II) is indicated by a flashing light; and the fact that the door has been violated (Condition III) is indicated by a flashing light and the concurrent sounding of an alarm.

A significant feature of the invention resides in the fact that voltage to momentarily actuate the indicators and alarm relays is obtained through internal console circuits, while the voltage to maintain the relays in the actuated state is obtained through circuits which include the wires to the remote stations, whereby resistance introduced by the wires does not impair the functioning of the associated relays. The reason for this is that while the full rated relay voltage is normally necessary to actuate a relay because of its inherent inertia and other factors, substantially less voltage is necessary to hold the relay in the actuated state. Thus the holding voltage necessary may be as much as to percent lower than that required to effect actuation.

Also an object of the invention is to provide a monitoring system of simple, reliable and efficient design which may be manufactured and sold at relatively low cost; Because the lines conducting relay current from the console to the various stations operate at low voltage levels, they offer no danger to building personnel nor do they constitute a fire hazard.

Briefly stated, these objects are accomplished in a monitoring system having a bank of relay-operated light indicators and a single relay-operated alarm device, each indicator relay being individually wired to a first switch at an associated remote door station, the alarm-device relay being wired to a second switch at the station, the various second switches being connected in series with respect to the alarm-device relay.

The arrangement is such that both switches at each station are closed when the door is closed, only the first switch is opened when the door is legally opened, and both switches are opened when the door is violated. Also included in the console is a flasher unit for the light indicators to cause them to provide periodic rather than steady illumination.

A light re-set switch is associated with the indicator relays to supply current thereto from a console supply, when this switch is momentarily closed, to energize the relays and thereby cause the indicators coupled to these relays to produce steady illumination. When any indicator relay is de-energized, a contact section thereof then connects the flasher unit to the associated light indicator to produce periodic illumination.

Momentary energization of the indicator relays causes another contact section thereof to connect the associated first door switches at the remote stations to holding circuits which maintain current flow through the relays only if the first door switch is closed, whereby when the first door switch is open, the associated light indicator is caused to flash to indicate a legal entry and when the first switch is closed, it is caused to produce steady illumination.

An alarm re-set switch is associated with the alarm relay. When this switch is momentarily closed, it acts to energize the alarm relay momentarily and thereby silence the alarm, for the alarm is connected to its current supply only when the alarm relay is de-energized. Momentary energization of said alarm relay causes a contact section thereon serially to connect all of the second door switches at the remote stations to a holding circuit which maintains current flow in said alarm relay to preserve alarm silence. But when any of these second switches opens as a result of a violation at the associated door, the alarm relay is deenergized to cause the alarm to sound at the console.

BRIEF DESCRIPTION OF DRAWING For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing, wherein:

FIG. 1 is a schematic representation of a monitoring system in accordance with the invention; and

FIG. 2 is a schematic circuit diagram of the system.

DESCRIPTION OF INVENTION The General Arrangement Referring now to FIG. 1, there is shown a monitoring system in accordance with the invention, the system being constituted by a console C located at a central point and operatively linked to a plurality of stations D D D etc. disposed at various remote points in a warehouse, a factory, or other building having access doors at each station.

The purpose of the monitor is to provide centralized indications of the status of the stations. Each station door is provided with a key-operated lock and switch assembly including two normally-closed switches S, and 8,. When the lock is legally unlatched by the key to open the door, only switch S, is opened thereby. When, however, the door is forced open illegally, switch S, as well as switch S, is opened thereby. Thus a status report on a particular station must account for three possible conditions:

CONDITION 1. Door closed (switches S, and S, both closed) CONDITION II. Door open legally (only switch S, open) CONDITION III. Door open illegally (switches S, and S, both open).

Console C is linked to the various stations by lines W extending between switches S, and S, and signal terminal board TB, and alarm terminal board TB respectively, each having a bank of terminal pairs thereon. Switch S in the first station D is connected to the first terminal pair in T8,, while switch S, in the same station is connected to the first terminal pair of TB, Corresponding connections are made for the S, and S, switches in the other stations.

By the way of example only, the terminal boards in FIG. 1 have each been provided with seven pairs of terminals. In practice, the system may be made in any desired capacity (as little as two stations, or as many as ten, twenty, fifty or even more). Mounted on the front panel of console C is a bank of light indicators L,, L,, L,, etc., there being as many lights as there are station terminal inputs. Housed behind the panel is a buzzer B, which gives an alarm under certain circumstances.

The arrangement is such that Condition I (door closed) at any station is indicated by constant illumination of the corresponding lamp L,, L etc. in the bank thereof. Condition II (door legally open) is indicated with respect to the same station by an intermittent illumination or flasher action of the corresponding light. Condition III (door violated) is indicated by a flasher action coupled with operation of the buzzer B, to sound an alarm calling attention to an illegal entry.

The Alarm Circuit The circuit arrangement of the monitoring system is shown in FIG. 2, in which station terminals TB, and TB are each provided, for purposes of simplicity, with only three pairs of terminals for door stations D,, D, and D Power for the system in one preferred embodiment thereof, is derived from an alternating-current (1 volt 60 cycle) power line and is stepped down by atransformer 10 to 12 volts AC.

The secondary oftransformer 10 is connected to a bridge rectifier circuit 11 whose l2-vo1t DC output appears at terminals T+ and T. The l2-volt AC output of the transformer is directly available at terminals l-lac and Lac, the first being the high side, and the second, the low side. One can, of course, just as well provide a battery-operated system, and the AC line-powered system is shown merely by way of example.

The light bulbs L L L etc. are energized by the l2-volt AC supply, while all relays in the system are of the DC type and are energized by the l2-volt DC supply. A bank of like light-operating relays R R R etc. is provided, there being as many relays as there are bulbs L L etc. and associated station terminals. When there are more terminal stations on the console than actual stations in use, jumpers are connected across the unused terminal pairs on terminals TB and TB, so that the lamps representing the unused stations always provide a closed door indication.

Initially, when themain power switch 12 in the primary oftransformer 10 is turned on, all relays R R R etc remain de-energized. The operation of buzzer B is controlled through a buzzer relay RB having two gangedarmatures 1 and 2 which engage the respective fixed upper contacts A when the relay is de-energized, and the respective fixed contact B when energized. Thus armature l and its contacts A and B represent one contact section of the buzzer relay RB andarmature 2 and its contacts A and B the other contact section.

Buzzer B, is connected between terminals Lac and Hac through armature l and its contact A of relay RB, thereby applying l2 volts AC to the buzzer when power is first turned on. In other words, as long as buzzer relay RB is de-energized, buzzer B is operative to give an alarm.

To initially silence the buzzer, a manually operated buzzerre-set switch 13 is depressed. This acts momentarily to complete a DC circuit between the coil of a relay RB and the l2-volt DC terminals T+ and T-, thereby energizing this relay and causingarmature 1 thereof to disengage from its A contact thus breaking the AC supply to the buzzer.

When relay RB is momentarily energized by operation of buzzerre-set switch 13,armature 2 thereof engages its associated contact B which is connected to one terminal in the last pair thereof on the alarm terminal block TB All pairs of terminals in alarm terminal block TB, are connected in series while shunted across each pair is the switch S, of the associated station. Switch S, is closed in Condition I, when the related door is closed, and also in Condition II, when the related door is legally opened.

The closed series connection formed by the terminal pairs in alarm terminal block T8,, combined with the closed door switches S, (Conditions I and II), provides an uninterrupted circuit betweenarmature 2 of buzzer relay RB, and the positive terminal T+ of the DC supply.Armature 2, when engaging its associated contact B is connected to one end of the coil of relay RB. The other end of this coil is permanently connected to terminal T.

Hence when relay RB is momentarily energized by depressing buzzerre-set switch 13, the resultant engagement ofarmature 2 and its B-contact maintains this relay in the energized state, and the buzzer remains silent as long as an unbroken series circuit exists in the series-connected terminals in the alarm terminal block TB.

But should any one of the switches-S, connected across the terminal pairs in TB, open as a result of Condition III (illegal entry), relay RB will be immediately de-energized, causingarmature 1 thereof to engage its A-contact and to re-establish the AC circuit of buuer B Thus the moment any one of the door alarm switches S, is opened in response to an illegal entry, the buzzer in the console will sound an alarm. The alarm, per se, does not identify the station of origin, this being effected by the light indication, in the manner to be later described. Obviously the alarm device need not be a buzzer and any other sound or lightproducing means may be used for this purpose.

It is important to note that the buzzer relay is initally energized by the internal console DC voltage supply circuit completed by closing buzzerre-set switch 13, and that it is thereafter held in the energized state by a holding circuit including the external lines extending to the switches S,. The fact that these external lines may be very long and thereby introduce a significant amount of resistance in the circuit, does not degrade the operation of the device, for it takes less voltage to maintain a relay energized, than it does to effect energization, for the latter requires the full rated voltage and the former, a significantly smaller amount. Hence the drop in voltage introduced by the long lines does not impair the circuit operation.

The Flasher Circuit:

Initially, when power is first turned on, all light bulbs L,, L,, L etc. will flash at a periodic rate (i.e., one-half second on one-half second off). The reason for this flashing action is as follows:

Relays R R R are provided with four contact sections formed by ganged armatures l, 2, 3 and 4, each acting in conjunction with respective upper contacts A and lower contacts B. The armatures normally engage the upper contacts A when the relays are de-energized. One end of light bulbs L,, L,, L etc. is connected toarmature 3 of light indicator relays R,, R,, R respectively, whereas the related A contacts of these relays are connected toarmature 1 of a flasher relay RF operating in conjunction with an upper contact A and a lower contact B. Armature l of flasher relay RF engages its associated A-contact when the relay is de-energized, this A-contact being connected to one A-C terminal l-lac. The other A-C terminal Lac is connected to all of the lamps L L and L,.

Hence intermittent actuation of flasher relay RF will cause AC current to flow intermittently to lamps L,, L, and L,. To effect intermittent actuation, the coil of flasher relay RF is connected to a uni-junction, solid-state, relaxation oscillator constituted bytransistors 14 and 15,resistors 16, 17 and 18, andcapacitor 19, the R-C constant of which is such as to provide periodic pulses at the desired flashing rate.

Direct current for the relaxation circuit of the flasher unit is provided by one line 20 going to the negative terminal T of the DC supply, and anotherline 21 going to armature 2 of relays R R R the associated A-contacts of which are connected to the positive terminal T+. Since initially all light indicator relays R R R are de-energized,armatures 2 thereof engage their associated upper contacts A, and at the outset, the flasher unit is operative to periodically energize relay RF and to cause a flashing operation of all lights.

To arrest this flashing action, a flasherre-set switch 22 is depressed momentarily. This switch, when closed, completes a DC connection between positive terminal T+ and through theuni-directional diodes 23, 24 and 25, to one end of the coils of relays R,, R R respectively, the other end of all the coils going through line 26 to negative terminal T-.

The Light Indicator Arrangement All relays (R R R etc.) are simultaneously energized when flasherre-set switch 22 is closed momentarily. When this happens, armatures l to 4 of these relays all engage their associated lower contacts B. Positive terminal T+ of the DC supply is connected throughdiodes 23, 24 and 25 to lower contacts B associated witharmature 4.

Armature 4 of relay R, is connected to one terminal of the first terminal pair of terminal block T8,, whilearmature 4 of relay R is connected to one terminal of the second terminal pair, andarmature 4 of relay R is connected to one terminal of the third terminal pair. The other terminals of the first, second and third terminal pairs of terminal blocks TB are all tied to the positive DC supply terminal T+.

When, therefore, relays R R R are momentarily energized by closingreset switch 22,armatures 2 thereof disengage their associated upper contacts A, thereby breaking the DC circuit between terminal T+ of the supply and the flasher unit. However, an uninterrupted AC from supply terminal Hac is applied to one end of lamps L,, L L through the actuatedarmatures 3 of relays R R R and their contact B, the other end of the lamps being permanently connected to terminal Lac.

It is to be noted that when the flahser re-set switch is momentarily depressed to cut ofi' the flasher circuit operation, full current is applied to relays R R R The current thereafter necessary to maintain these relays energized is obtained through the external lines from the terminal pairs on TB going to switches S, on the door stations. Even though these lines may be extended and introduce a substantial resistance in the circuit of the related relay coil, the relay will remain energized, for full current is required only for actuating the relays, not for holding them.

Thus far we have considered the behavior of the system for Condition l, in which all switches S, and S, at the several stations are closed. In this condition, after the power is turned on and the buzzer re-set, switch B and the flasherre-set switch 22 are momentarily closed, we have a situation in which all lamps L,, L L etc. are steadily illuminated and buzzer B is silent to indicate that all doors are properly closed.

Let us now consider the behavior of the system for Condition ll, in which a door, say, at station D is legally opened by a proper key. When that happens, switch S, at station D will open, thereby opening the circuit between the second terminal pair on TB, and breaking the DC holding circuit to the coil of relay R througharmature 4 and contact B.

The resultant de-energization of relay R causes the armatures thereof to engage upper contacts A. Hence lamps L, will now be energized througharmature 3 and contact A of relay R,, which will connect this lamp in series witharmature 1 and contact A of the flasher relay RF, whose flasher circuit will now be energized througharmature 2 and associated contact A of relay R Thus all lights other than lamp L, will remain steadily illuminated, while lamp L is flash-operated, thereby indicating a legal entry at door D Depressing flasher re-set switch 22 will only momentarily actuate relay R for this relay cannot be held in the energized state for its holdingarmature 4 gets its current through the second terminal pair of terminal block TR,, which is open-circuited because the related switch S, is open. When, however, the legally opened door is subsequently closed, thereby closing the related switch 8,, the bulb L will cease to flash and remain in the steady-state of illumination. In short, when a particular lamp provides steady illumination this indicates that its corresponding door is closed and when the same lamp begins to flash this indicates that the door is open.

The circuit of alarm buzzer B is in no way affected by relays R,, R R for its operation is entirely under the control of the switches 8,, connected to the terminal pairs on alarm terminal board T8,, and the buzzer relay is responsive only when one of switches S, opens, without regard to what happens to switches 8,.

Let us finally consider the behavior of the system for Condition Ill, when both switches S, and S, are opened at a particular door station as a result of an illegal entry. This violation is indicated by the flashing of the related light, which is brought about by the opening of switch S, in the manner described in connection with Condition ll, accompanied by the sounding of the buzzer alarm by reason of the concurrent opening of switch 5,.

A feature of the alarm circuit residesin the fact that after a violation occurs, the operator can silence buzzer B, by depressing the buzzerre-set switch 13, which will cause energization of buzzer relay RB and cut off current to the buzzer. The flashing light which represents the violated station will, however, continue to flash, and the buzzer is now prepared to sound off should a violation take place at another door.

While a preferred embodiment of the invention has been disclosed, many changes and modifications may be made therein within the spirit of the invention. Thus in place of electromechanical relays one may use equivalent solid state devices.

What I claim is:

l. A monitoring system in which a central console is wired to remote door stations, each station being provided with a first switch which is closed when the door is closed and is opened when the door is opened legally, said console comprising:

A. a bank of light indicators equal in number to the number of first switches,

B. An electromechanical relay for operating each indicator,

said relay having contact sections,

C. a light re-set switch connected to said indicator relays to supply energizing current thereto from a console supply to actuate same when the switch is momentarily closed, one of said contact sections of each relay then acting to supply current to the light indicator associated therewith to produce a steady illumination,

D. means connecting the first switch at each station to the corresponding relay through another contact section thereof to supply a holding current thereto to maintain said relay energized and thereby to operate the associated light indicator to provide steady illumination as long as said first switch is closed, said relays being de-energized when said first switch is open,

E. a flasher unit for said light indicators, and

F. means to connect said flasher unit to that indicator whose relay is de-energized, to provide periodic illumination indicating that the first switch is open whereby in the condition when the door at any station is closed the related light indicator on the console provides steady illumination to indicate this condition, and in another condition when the dor is legally opened the same light indicator is periodically illuminated to indicate that condition.

2. A system as set forth inclaim 6, wherein said relays are electromechanical devices which require an actuating voltage whose magnitude is greater than the voltage required to hold it in the energized state.

3. A system as set forth inclaim 6, wherein said relays are solid state devices.

4. A system as set forth inclaim 6, wherein said alarm is a buzzer.

5. A system as set forth inclaim 6, wherein said flasher unit includes a solid state relaxation oscillator whose output is applied to a relay to produce a periodic switching action.

6. A monitoring system in which a central console is wired to remote door stations, each station being provided with a first switch which is closed when the door is closed and is opened when the door is legally opened, and a second switch which is opened only when the door is illegally opened, said console comprising:

A. a bank of light indicators equal in number to the number of first switches,

B. a relay for operating each indicator, said relay having contact sections,

C. a light re-set switch connected to said indicator relays to supply energizing current thereto from a console supply to actuate same when the switch is momentarily closed, one of said contact sections of each relay then acting to supply current to the light indicator associated therewith to produce a steady illumination,

D. means connecting the first switch at each station to the corresponding relay through another contact section thereof to supply a holding current thereto to maintain said relay energized and thereby to operate the associated light indicator to provide steady illumination indicating a closed door condition as long as said first switch is closed, said relay being de-energized when said first switch is open,

E. a flasher unit for said light indicators,

F. means to connect said flasher unit to that indicator whose relay is de-energized, to provide periodic illumination indicating that the first switch is open as a result of a legal opening of the door,

G. an alarm device,

H. an auxiliary relay for operating said device, said auxiliary contact sections and acting to supply current to said alarm device only when the auxiliary relay is de-energized thereby to sound the alarm, and

J. means connecting the second switches of all door stations in series with another contact section of said auxiliary relay in a holding circuit to maintain said auxiliary relay energized after it is momentarily actuated, whereby when any of said second switches opens as a result of an illegal opening of the door, said alarm is sounded.

7. A monitoring system in which a control console is wired to remote door stations, each station being provided with a first switch which is closed when the door is closed and is opened when the door is opened either legally or illegally, and a second switch which is closed when the door is closed and is opened only when the door is opened illegally, said console comprising:

A. a bank of indicators equal in number to the number of stations,

B. an alarm,

C. means connecting said first switches at each station to the corresponding indicators in said bank thereof to cause each indicator to represent either a first condition in which the door at the associated station is closed or a second condition in which the door is legally or illegally opened, and I D, means connecting said second switches to said alarm to activate said alarm when any one of said second switches is opened, thereby affording notice of a third condition in which a door at any station is illegally opened.

Claims (7)

1. A monitoring system in which a central console is wired to remote door stations, each station being provided with a first switch which is closed when the door is closed and is opened when the door is opened legally, said console comprising: A. a bank of light indicators equal in number to the number of first switches, B. An electromechanical relay for operating each indicator, said relay having contact sections, C. a light re-set switch connected to said indicator relays to supply energizing current thereto from a console supply to actuate same when the switch is momentarily closed, one of said contact sections of each relay then acting to supply current to the light indicator associated therewith to produce a steady illumination, D. means connecting the first switch at each station to the corresponding relay through another contact section thereof to supply a holding current thereto to maintain said relay energized and thereby to operate the associated light indicator to provide steady illumination as long as said first switch is closed, said relays being de-energized when said first switch is open, E. a flasher unit for said light indicators, and F. means to connect said flasher unit to that indicator whose relay is de-energized, to provide periodic illumination indicating that the first switch is open whereby in the condition when the door at any station is closed the related light indicator on the console provides steady illumination to indicate this condition, and in another condition when the dor is legally opened the same light indicator is periodically illuminated to indicate that condition.

2. A system as set forth in claim 6, wherein said relays are electromechanical devices which require an actuating voltage whose magnitude is greater than the voltage required to hold it in the energized state.

3. A system as set forth in claim 6, wherein said relays are solid state devices.

4. A system as set forth in claim 6, wherein said alarm is a buzzer.

5. A system as set forth in claim 6, wherein said flasher unit includes a solid state relaxation oscillator whose output is applied to a relay to produce a periodic switching action.

6. A monitoring system in which a central console is wired to remote door stations, each station being provided with a first switch which is closed when the door is closed and is opened when the door is legally opened, and a second switch which is oPened only when the door is illegally opened, said console comprising: A. a bank of light indicators equal in number to the number of first switches, B. a relay for operating each indicator, said relay having contact sections, C. a light re-set switch connected to said indicator relays to supply energizing current thereto from a console supply to actuate same when the switch is momentarily closed, one of said contact sections of each relay then acting to supply current to the light indicator associated therewith to produce a steady illumination, D. means connecting the first switch at each station to the corresponding relay through another contact section thereof to supply a holding current thereto to maintain said relay energized and thereby to operate the associated light indicator to provide steady illumination indicating a closed door condition as long as said first switch is closed, said relay being de-energized when said first switch is open, E. a flasher unit for said light indicators, F. means to connect said flasher unit to that indicator whose relay is de-energized, to provide periodic illumination indicating that the first switch is open as a result of a legal opening of the door, G. an alarm device, H. an auxiliary relay for operating said device, said auxiliary relay having contact sections, I. an alarm re-set switch connected to said auxiliary relay contact sections and acting to supply current to said alarm device only when the auxiliary relay is de-energized thereby to sound the alarm, and J. means connecting the second switches of all door stations in series with another contact section of said auxiliary relay in a holding circuit to maintain said auxiliary relay energized after it is momentarily actuated, whereby when any of said second switches opens as a result of an illegal opening of the door, said alarm is sounded.

7. A monitoring system in which a control console is wired to remote door stations, each station being provided with a first switch which is closed when the door is closed and is opened when the door is opened either legally or illegally, and a second switch which is closed when the door is closed and is opened only when the door is opened illegally, said console comprising: A. a bank of indicators equal in number to the number of stations, B. an alarm, C. means connecting said first switches at each station to the corresponding indicators in said bank thereof to cause each indicator to represent either a first condition in which the door at the associated station is closed or a second condition in which the door is legally or illegally opened, and D. means connecting said second switches to said alarm to activate said alarm when any one of said second switches is opened, thereby affording notice of a third condition in which a door at any station is illegally opened.

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